feat: add mil and inch units to plot_length_units

[yaugenst-flex]

Partially addresses #2644

@yuanshen-flexcompute FYI we already had "in" in constants, but it wasn't registered as a LengthUnit for plots, hence I didn't rename it.

[greptile-apps]

Reviewing changes made in this pull request

[github-actions]

Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/types.py (100%)
• tidy3d/components/viz/axes_utils.py (38.3%): Missing lines 29-30,34,38-39,42-43,45,47,50-51,53-56,61,64-65,70-71,73,76-77,80-81,84,91,94-95

Summary

• Total: 48 lines
• Missing: 29 lines
• Coverage: 39%

tidy3d/components/viz/axes_utils.py

  25             super().__init__()
  26             self.scale_factor = scale_factor
  27 
  28         def __call__(self):
! 29             vmin, vmax = self.axis.get_view_interval()
! 30             return self.tick_values(vmin, vmax)
  31 
  32         def view_limits(self, vmin, vmax):
  33             """Override to prevent matplotlib from adjusting our limits."""
! 34             return vmin, vmax
  35 
  36         def tick_values(self, vmin, vmax):
  37             # convert the view range to the target unit
! 38             vmin_unit = vmin * self.scale_factor
! 39             vmax_unit = vmax * self.scale_factor
  40 
  41             # tolerance for floating point comparisons in target unit
! 42             unit_range = vmax_unit - vmin_unit
! 43             unit_tol = unit_range * 1e-8
  44 
! 45             locator = ticker.MaxNLocator(nbins=11, prune=None, min_n_ticks=2)
  46 
! 47             ticks_unit = locator.tick_values(vmin_unit, vmax_unit)
  48 
  49             # ensure we have ticks that cover the full range
! 50             if len(ticks_unit) > 0:
! 51                 if ticks_unit[0] > vmin_unit + unit_tol or ticks_unit[-1] < vmax_unit - unit_tol:
  52                     # try with fewer bins to get better coverage
! 53                     for n in [10, 9, 8, 7, 6, 5]:
! 54                         locator = ticker.MaxNLocator(nbins=n, prune=None, min_n_ticks=2)
! 55                         ticks_unit = locator.tick_values(vmin_unit, vmax_unit)
! 56                         if (
  57                             len(ticks_unit) >= 3
  58                             and ticks_unit[0] <= vmin_unit + unit_tol
  59                             and ticks_unit[-1] >= vmax_unit - unit_tol
  60                         ):
! 61                             break
  62 
  63                 # if still no good coverage, manually ensure edge coverage
! 64                 if len(ticks_unit) > 0:
! 65                     if (
  66                         ticks_unit[0] > vmin_unit + unit_tol
  67                         or ticks_unit[-1] < vmax_unit - unit_tol
  68                     ):
  69                         # find a reasonable step size from existing ticks
! 70                         if len(ticks_unit) > 1:
! 71                             step = ticks_unit[1] - ticks_unit[0]
  72                         else:
! 73                             step = unit_range / 5
  74 
  75                         # extend the range to ensure coverage
! 76                         extended_min = vmin_unit - step
! 77                         extended_max = vmax_unit + step
  78 
  79                         # try one more time with extended range
! 80                         locator = ticker.MaxNLocator(nbins=8, prune=None, min_n_ticks=2)
! 81                         ticks_unit = locator.tick_values(extended_min, extended_max)
  82 
  83                         # filter to reasonable bounds around the original range
! 84                         ticks_unit = [
  85                             t
  86                             for t in ticks_unit
  87                             if t >= vmin_unit - step / 2 and t <= vmax_unit + step / 2
  88                         ]

---

  87                             if t >= vmin_unit - step / 2 and t <= vmax_unit + step / 2
  88                         ]
  89 
  90             # convert the nice ticks back to the original data unit (micrometers)
! 91             ticks_um = ticks_unit / self.scale_factor
  92 
  93             # filter to ensure ticks are within bounds (with small tolerance)
! 94             eps = (vmax - vmin) * 1e-8
! 95             return [tick for tick in ticks_um if vmin - eps <= tick <= vmax + eps]
  96 
  97     return UnitAwareLocator
  98 

---

[yuanshen-flexcompute]

Overall looks good. One minor quibble: when using metric units, e.g. 'mm', the plot functions show nice round numbers in the axis ticks:

However, when switching to 'mil', the tick locations don't change, resulting in ugly numbers:

Is it possible to change the plot functions to show nicer tick numbers in 'mil' or 'in'?

Thanks.

[yaugenst-flex]

@yuanshen-flexcompute fixed!

[daquinteroflex]

Looks good! Users of imperial units will be thrilled